Surface antigens are being extracted from exponential phase cultures of Actinomyces viscosus T14V and T14AV. Those antigens found to be unique to the virulent strain (T14V) are being purified and tested for biological activity in lymphoblast assays and in a germ-free mouse model. The in situ localization of the extracted antigens is being examined by specific labeling of surface components with 125I with subsequent localization in electrophoresis gels. Ultrastructural examination of both virulent (T14V) and avirulent (T14AV) strains by transmission and scanning electron microscopy has been most useful in understanding the possible avenues resulting in differential virulence for the germ-free rat system. The virulent strain possesses surface structures (and antigens) absent in the avirulent strain. Clinical isolates of A. viscosus are being obtained and tested for the presence of the virulence-associated antigens of T14V by immunoelectrophoresis of chemical extracts into antiserum-containing gels. These results will indicate the prevalence of these unique antigens in the natural population. Once this prevalence has been established, the analysis will be expanded to determine whether or not a correlation exists between the incidence of virulence antigens and gingival or periodontal health.